Method for forming composite arrays of single-wall carbon nanotubes and compositions thereof

ABSTRACT

Macroscopically manipulable nanoscale devices made from nanotube assemblies are disclosed. The article of manufacture comprises a macroscopic mounting element capable of being manipulated or observed in a macroscale environment, and a nanoscale nanotube assembly attached to the mounting element. The article permits macroscale information to be provided to or obtained from a nanoscale environment. A method for making a macroscopically manipulable nanoscale devices comprises the steps of (1) providing a nanotube-containing material; (2) preparing a nanotube assembly device having at least one carbon nanotube for attachment; and (3) attaching said nanotube assembly to a surface of a mounting element.

TECHNICAL FIELD OF THE INVENTION

[0001] This invention relates generally to the field of macroscopicallymanipulable nanoscale devices that permit information to be provided toor obtained form a nanoscale environment, and more particularly to theuse of nanotubes attached to macroscale mounting members as nanoscaleprobes, fabricators and manipulators.

BACKGROUND OF THE INVENTION

[0002] The development of mechanical, electrical, chemical andbiological devices and systems that include or comprise nanoscalecomponents, sometimes termed nanotechnology, has been slowed by theunavailability of or limitations inherent in devices that enablesensing, measuring, analyzing, and modifying objects with nanometerresolution and sensing, measuring, analyzing, moving, manipulating,fabricating and modifying objects with nanometer dimensions.

[0003] One class of devices that have found some use in nanotechnologyapplications are proximity probes of various types including those usedin scanning tunneling microscopes (STM), atomic force microscopes (AFM)and magnetic force microscopes (MFM). While good progress has been madein controlling the position of the macroscopic probe to sub-angstromaccuracy and in designing sensitive detection schemes, the tip designsto date have a number of problems.

[0004] One such problem arises from changes in the properties of the tipas atoms move about on the tip, or as the tip acquires an atom ormolecule from the object being imaged. Another difficulty with existingprobe microscope tips is that they typically are pyramidal in shape, andthat they are not able to penetrate into small “holes” on the objectbeing imaged, and they may give false image information around sharpvertical discontinuities (e.g., steps) in the object being imaged,because the active portion of the “tip” may shift from the bottom atomto an atom on the tip's side. Moreover, conducting conventional probemicroscope tips have never been successfully covered with an insulatingmaterial so that the only electrically-active element is the point ofthe tip itself.

[0005] Conventional probe microscope tips also are very rigid incomparison to many of the objects to be examined, and with “soft”samples (e.g., biomolecules like DNA) conventional AFM tips misrepresentthe thickness of the object imaged, because that object is literallycompressed by the action of the tip.

[0006] Thus, there is a need for macroscopically manipulable nanoscaledevices for observing, fabricating or otherwise manipulating individualobjects in a nanoscale environment that address the foregoing and otherdisadvantages of the prior art.

SUMMARY OF THE INVENTION

[0007] The present invention employs geometrically-regular molecularnanotubes (such as those made of carbon) to fabricate devices thatenable interaction between macroscopic systems and individual objectshaving nanometer dimensions. These devices may comprise one or moreindividual nanotubes, and/or an assembly of nanotubes affixed to asuitable macroscopically manipulable mounting element whereby the devicepermits macroscale information to be provided to or obtained from ananoscale environment.

[0008] Indivdual nanotubes or bundles of nanotubes can be recovered froma material (such as the carbon nanotube “ropes”) grown by proceduresdescribed herein. Assemblies of nanotubes can be fabricated by physicalmanipulation of nanotube-containing material, or by self-assembly ofgroups of nanotubes, or by chemical physical or biological behavior ofmoieties attached to the ends or to the sides of the nanotubes orbundles of nanotubes. Individual nanotubes or assemblies of nanotubescan be grown to achieve specific characteristics by methods describedherein.

[0009] More particularly, the devices of the present invention cancomprise probes with tips comprising one or more molecular nanotubes.When attached to an appropriate motion transduce (piezoelectricmagnetic, etc.) the probe is capable of sensing, measuring, analyzing,and modifying objects with nanometer resolution and sensing, measuring,analyzing, moving, manipulating, and modifying objects with nanometerdimensions.

[0010] A method for making such devices is disclosed, which includes thesteps of (1) providing a nanotube-containing material; (2) preparing ananotube assembly comprising at least one nanotube from thenanotube-containing material; and, (3) attaching the nanotube assemblyto a macroscopically manipulably mounting element.

[0011] The nanoscale devices according to the present invention providestrong, reliably mounted probe tips and other nanoscale fabricators andmanipulators, that are gentle, hard to damage, even upon “crashing” intothe working surface, that can be easily made electrically conductive,that can present a uniform diameter and precisely known atomicconfiguration, including precisely located derivitization with chemicalmoieties.

[0012] The devices of the present invention have a number of advantagesover conventional microscopy probes (e.g. STM and AFM). A probe tipconsisting of a single molecular nanotube or a few such tubes has theadvantage that all its constituent atoms are covalently bonded in placeand are unlikely to move, even under extreme stress, such as thatoccurring when the tip “crashes” into the object being imaged. Moreover,the known, stable geometry of molecular nanotube tips allows one to moreaccurately interpret the data acquired by probe microscopes using suchtips. In addition, molecular nanotubes are very compliant, buckling in agentle, predictable, and controllable fashion under forces that aresmall enough to avoid substantial deformation to delicate sampleobjects. Unlike currently used pyramidal probe tips, molecular nanotubesare very long with respect to their diameter, and can therefore reliablyimage the bottom areas of holes and trenches in the items being imaged.

[0013] Electrically conducting nanotube tips can be coated with aninsulating material to achieve localized electrical activity at the endof the probe element. This geometry facilitates probing ofelectrochemical and biological environments.

[0014] Molecular nanoprobe elements have remarkably different chemicalactivity at their ends because the atomic configuration on the endsdiffers fundamentally from that of the sides. Consequently, one canselectively bond specific molecules to the tip end. This site specificbonding enables chemically-sensitive probe microscopy, and a form ofsurface modification in which some superficial atoms or molecules of theobject being imaged react chemically with the probe tip or speciesattached or bonded to it. This delicate chemistry enables a form ofsurface modification that is not possible with conventional tips. Thissurface modification can serve as a direct manipulation technique fornanometer-scale fabrication, or as a method of lithography in which a“resist” is exposed by the chemical or electrochemical action of thetip.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] For a more complete understanding of the present invention, theobjects and advantages thereof, reference is now made to the followingdescriptions taken in connection with the accompanying drawings inwhich:

[0016]FIGS. 1a-e illustrate various embodiments of probe tips accordingto the present invention.

[0017]FIGS. 2a-c show a typical nanotube probe according to oneembodiment of the invention.

[0018]FIG. 3a shows the frequency dependency of the amplitude of a SFMwith an nanotube tip engaged in tapping mode.

[0019]FIG. 3b shows the result of a direct numerical simulation using abuckling force equation.

[0020]FIGS. 4a-d illustrates the probing capabilities of nanotube tips.

[0021]FIGS. 5a-b show the frequency dependency of a cantilever having ananotube probe immersed in water.

[0022]FIG. 6 shows an example of atomic-scale resolution STM using acarbon nanotube to image the charge density waves on a freshly cleaved1T-TaS2 surface.

[0023]FIG. 7A is a TEM/SEM/Raman spec of purified SWNTs useful in thepractice of the present invention.

[0024]FIG. 7B is a TEM/SEM/Raman spec of purified SWNTs useful in thepractice of the present invention.

[0025]FIG. 7C is a TEM/SEM/Raman spec of purified SWNTs useful in thepractice of the present invention.

[0026]FIG. 8 is a schematic representation of a portion of anhomogeneous SWNT molecular array useful in the practice of the presentinvention.

[0027]FIG. 9 is a schematic representation of an heterogeneous SWNTmolecular array useful in the practice of to the present invention.

[0028]FIG. 10 is a schematic representation of the growth chamber of thefiber apparatus useful in the practice of to the present invention.

[0029]FIG. 11 is a schematic representation of the pressure equalizationand collection zone of the fiber apparatus useful in the practice of tothe present invention.

[0030]FIG. 12 is a composite array useful in the practice of the presentinvention.

[0031]FIG. 13 is a composite array useful in the practice of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

[0032] The preferred embodiment of the present invention and itsadvantages are best understood by referring to FIGS. 1 through 13 of thedrawings, like numerals being used for like and corresponding parts ofthe various drawings.

[0033] Macroscopically Manipulable Nanoscale Devices

[0034] Broadly, the macroscopically manipulable nanoscale devices of thepresent invention comprise a nanotube assembly attached to a mountingelement that permits macroscopic manipulation or observation. In apreferred form this device comprises a nanotube probe tip assembly madeup of one or more single-wall and/or multi-wall nanotubes. This assemblyis connected to a mounting element at one end, with the other end beingfree and capable of coming into direct contact or near proximity to theobject being sensed, measured, an, moved, manipulated, and/or modified.The free “sensing end” has a transverse dimension in the nanometerrange. The “sensing end” interacts with objects being sensed, measured,analyzed, moved, manipulated, and/or modified by means which are (eitherindividually or in combination) physical, electrical, chemicalelectromagnetic, or biological. These interactions produce forces,electrical currents, or chemical compounds which reveal informationabout the object and/or modify that object in some way.

[0035] Mounting Element

[0036] The mounting element facilitates the transduction of informationbetween the macroscopic and nanoscopic worlds. The mounting elementsupports and moves the probe, and may provide electrical connections tothe probe. In addition, the mounting element may serve as a transducerthat converts a physical, chemical, electrical, mechanical, or opticalresponse of the probe itself to another form that is more readilydetectable by instrumentation known to those skilled in the art of probemicroscopy. The mounting element also serves to enable the probe'smotion and to facilitate its action in the sensing, measuring,analyzing, moving, manipulating, and modifying other objects.

[0037] For many analytical applications, the currently employed mountingsystems can be employed in carrying out the present invention. In thisregard, the cantilever or probe tip of various known proximity probessuch as STM, AFM and MFM devices can serve as the mounting element ofthe present invention. These devices typically provide for observationof or activation by macroscopically manipulable forces, using sensingmethods that typically measure the deflection of the mounting element(e.g., cantilever) by electronic (e.g., tunneling current), optical(e.g, optical interferometry or beam deflection, or electro mechanical(e.g., piezoelectric) elements. For the structure and operation of suchconventional mounting elements, reference can be made to the following,all of which are hereby incorporated by reference in their entirety:Marcus et al. U.S. Pat. No. 5,475,318 Beha et al. U.S. Pat. No.4,918,309 Jain et al. U.S. Pat. No. 5,566,987 Burnham et al. U.S. Pat.No. 5,193,383

[0038] In the devices described in these references and others ofsimilar function and structure, the present invention contemplatesreplacing or augmenting the probe tip, or surface interaction element,with a nanotube assembly as described below.

[0039] Nanotube Assembly

[0040] The nanotube assembly of the present invention can be formed fromany geometrically regular molecular nanotubes, and is preferablyprepared from isolated, purified carbon nanotubes produced by any of themethods described herein. The carbon nanotube can be multi-wail orsingle-wall, with single-wall carbon nanotubes being preferred. Thesingle-wall carbon nanotube can be of the metallic type, i.e. arm chairor (n,n) in configuration or of the insulating type, i.e. (m,n) inconfiguration. For applications requiring electrical conductivity, themost preferred are (10,10) SWNTs. The carbon nanotubes may besubstituted, i.e., have lattice atoms other than C (e.g. BN systems) orexternally derivitized by the addition of one or more chemical moietiesat either a side location, an end location, or combinations. The carbonnanotubes may also be endohedrally modified by including one or moreinternal species inside the tube structure. Suitable endohedral speciesinclude metals (e.g. Ni, Co, Yb), ions, small molecules and fullerenes.Endohedral species may have magnetic properties (i.e. ferromagnetic,paramagnetic), electrochemical properties, optical properties, or othersuitable properties.

[0041] The structure of the nanotube assembly can vary depending on thepurpose for which the device is used. In many cases, a single nanotubewill serve as the nanotube assembly. Referring to FIG. 1a, such anassembly is shown. Nanotube assembly 100 consists of a mounting element104 with a single nanotube 102 attached thereto. Small bundles ofgenerally parallel and coterminating nanotubes containing from about2-100 nanotubes, preferably about 2 to about 20 nanotubes and mostpreferably about 5 to about 10 nanotubes, can also be employed. (SeeFIG. 1b). This assembly 120 consists of a bundle of nanotubes 122. Thisbundle 122 can be held together by van der Waals forces or otherwisebound together.

[0042] In one preferred embodiment shown in FIG. 1c, a bundle ofnanotubes 142 forming the nanotube assembly 140 includes at least onenanotube 144 that extends beyond the end of the other nanotubes in thebundle. This extension can result from employing at least one longernanotube or bonding an extension length to the end of the bundle (i.e.to one of the bundle length nanotubes). Also, as shown in FIG. 1d anddescribed below, the nanotube assembly 160 may be coated (preferablyafter attachment to the mounting element) with a suitable material 164.

[0043] The diameter of the nanotube assembly can be uniform along itslength (as in the embodiment of FIG. 1(a) and 1(b) or non uniform alongits length (as in the embodiments of FIG. 1(c) and (d)). Even in thelatter forms it is preferred that the tip section of FIGS. 1(c) and (d)respectively is of uniform diameter. Useful diameters can range from afew nm (for single tubes) up to about 100 nm for ropes or bundles.Preferred are bundles having diameters of about 2 nm to about 50 nm, andmost preferred are diameters of about 5 nm to about 20 nm.

[0044] The total length of the nanotube assembly can be from about 1 to100 times its diameter, preferably greater than 20 times its diameter.In general, lengths of from about 50 to about 10,000 nm are employed,depending on the nature of the device and its intended environment ofoperation. For probes (e.g. STM, AFM) the nanotube assembly should befrom about 50 nm to 5000 nm in length with about 300 nm to about 500 nmbeing preferred. For structures of the type shown in FIG. 1(c) thesingle nanotube tip portion can extend for up to ½ or more of the lengthof the total assembly. For example, a 550 nm long tip of the type shownin FIG. 1(c) has a body section 142 of about 300 nm and a tip section144 of about 250 nm.

[0045] Method of Attaching a Nanotube Assembly to a Mounting Element

[0046] In another embodiment, a method for attaching a nanotube assembly(which can include a single nanotube or a bundle, e.g, a rope ofnanotubes) to a mounting element is provided. Fundamental to themounting process is the surprising realization that the nanotubes, whichin two dimensions are substantially smaller than the wavelength ofvisible light (even when several run alongside each other in a thickerbundle), may nevertheless be adequately perceived with an opticalmicroscope to permit their observation and mounting. This observabilityunder visible illumination is possible because, for the component oflight which is polarized along the length of the nanotube (in whichdirection the nanotubes are longer than the wavelength of visiblelight), where this component has adequate intensity and the scatteringfrom other objects is minimized to permit contrast, the nanotubesscatter light with sufficient efficiency to be rendered observable.

[0047] In the case of through the objective lens illumination utilizingunpolarized white light, the source must be made so intense that evenwith high quality anti-reflection coated optics, reflections fromoptical component surfaces and the scattering of light fromimperfections in the optical components renders the contrast too poor topermit observation of individual nanotubes or thin bundles. Thislimitation is largely circumvented by application of the dark fieldtechnique; however, even with the advantages that this provides,confirmation that a very thin sample, which appears to the dark adaptedeye as the barest visible ghost of an image, requires a sensitive cameracapable of integrating the image (operationally, for quick assessment anelectronic device such as a CCD camera, rather than film is desirable).Alternatively, a thin laser beam, polarized along the direction of thenanotube is passed through an off axis portion of the objective lenswhere the back reflections from optical components are directed out ofthe field of view and imperfections in the components are avoided (asindicated by minimizing the degree of extraneous field illumination asthe beam is moved around to different portions of the objective).Alternatively, light (white or laser) is trained on the sample from aside perpendicular to the axis of the nanotube such that lightscattering off the nanotube enters the microscope objective. In allthese cases the visibility of the sample is greatly enhanced when theorientation of the nanotube, relative to the propagation direction ofthe illumination and the optic axis of the microscope are arranged as ifa mirror resides in the plane of the nanotube, oriented such as tomaximize the specular reflection of the source into the field of view ofthe microscope.

[0048] The first step in the method of this invention is to provide ananotube-containing material. As discussed below, there are severaltechniques for preparing these materials. The next step in the processinvolves preparation of the nanotube assembly. For assemblies made ofsingle nanotubes or bundles of nanotubes this step may compriseseparating an individual nanotube or bundle form a material containingthese forms. For example, for raw arc grown boule, a small piece ofboule material can be ripped from the as grown deposit and attached toits mount using double-sided tape. For oxygen purified material, a smallpiece may similarly be ripped from the purified boule. Individualnanotubes and bundles which stick out from this piece of boule(outliers) are then available for attachment to the mounting device.Generally it is found that such a sample presents few outliers and theyare often too well embedded in the dense piece of boule to permitpulling out. More opportunities are presented if the raw boule materialis ground into roughly 10-100 μm chunks which are then picked up bydouble-sided tape. In another embodiment, the nanotube assembly cancomprise carbon fibers grown from SWNT molecular arrays as describedbelow. Carbon fibers grown using the random growth of carbon fibers fromSWNTs as described below, also may be used.

[0049] The next step in the method of this invention involves attachingto (mounting) the nanotube assembly to the mounting element. Themounting procedure requires at minimum two precision XYZ translationstages, stages A and B. These stages must be arranged such that thesharp point or edge of the mounting element to which the nanotubeassembly (single or bundle) is to be mounted is supported by one of thetranslation stages in the field of view of the microscope (stage A),while a mass of nanotubes from which the nanotube sample is to be culledis similarly supported in the microscope field of view by the secondtranslation stage B. Manual actuators for these stages are adequate forthe mounting, however, for some applications, additional final samplepreparation steps require the use of electromechanical actuators.

[0050] It is found that the number of outliers available for attachmentis greatly enhanced if the surface of the piece of boule has a piece oftape gently touched to it such that nanotubes become embedded in theadhesive layer and the tape is then lifted off in a directionperpendicular to the surface, pulling out a layer of nanotubes tens ofmicrons thick. The tug of war between the nanotubes on either side ofthe boundary layer separating the two newly formed surfaces (one on theremaining piece of boule and the other on the piece of tape) has theeffect of orienting the exposed nanotubes perpendicular to each newsurface thus generating the numerous outliers. In an alternateembodiment, it may be desirable to mount the piece of tape on stage Band then to cull the nanotube sample from this material.

[0051] For mounting the nanotube sample onto the mounting device, aselected outlier is situated in the field of view of the microscopewhile the appropriate tip or edge of the mounting device is brought upalongside the outlier such that there is appreciable overlap. Themounting device or outlier is then translated in such a manner thatcontact is made between the two over the length of the overlap.Attachment of the outlier to the mounting device tip with sufficientbond strength to permit the nanotube sample to be detached from the massof nanotubes affixed on stage B may be effected in several ways.

[0052] In a preferred embodiment, the force of attachment is provided bythe van der Waals bonding between the nanotube sample and the surface ofthe mounting device. For this to be sufficiently strong to extract thesample, the surface of the mounting device must have large sectionswhich are smooth and regular on an atomic scale permitting intimatecontact between the nanotube sample surface(s) and the device surface. Ahighly graphitized carbon fiber (commercially available) is an exampleof such a device, which being electrically conducting additionallyprovides for electrical connection to the nanotube. The graphitic natureof the surface in this case makes the total bond strength particularlystrong since the atomic registration between the graphene surface ofnanotubes and the graphitic surface of the fiber permits particularlyintimate contact over more atoms per unit area than any other surface.

[0053] Once intimate contact between the sample and the mounting devicehas been made, the mounting device is translated in a direction awayfrom the nanotube layer. Often, when the bond strength of the nanotubesample to the mounting device tip surface exceeds the strength of itsbonds to other nanotubes that it contacts on the tape side layer, thenanotube sample is extracted from the layer and now freely attached tothe mounting device.

[0054] For some applications, it is necessary to have the tip of thenanotube sample extend further from the point of attachment on themounting device than the typical length of the extracted sample yields.In such cases a longer sample is generated by attaching one nanotubesample and then repeating the above procedures with the tip of thissample treated as the tip of the mounting device. This may be repeatedas often as desired. This procedure may also be applied when thenanotube sample consists of a bundle of nanotubes which end closetogether but a single nanotube tip sample, of longer single nanotubelength, is desired. In that case the last outlier attached should bevery faint and uniform in the intensity of its light scatteredindicating it to be a single nanotube.

[0055] In another preferred embodiment, the tip of the mounting deviceto which the nanotube sample is to be attached is pretreated with a thinadhesive layer before contact to the nanotube sample is made. Theadhesive can be one which must cure like an epoxy resin in order to forma bond or one which remains tacky. An example of the latter is providedby the adhesive layer on the double sided tape which is used to affixthe nanotube mass to its mount on stage B. This is particularlyconvenient because the thin adhesive layer can be applied to the tip ofthe mounting device, in situ, under microscopic observation, just priorto nanotube sample contact. To accomplish this, the mounting device tipis translated to a nanotube free region of the tape, where the tip isthen driven a few microns into the adhesive layer and subsequentlywithdrawn, pulling out with it a thin layer of the adhesive which hascoated the tip. Contact with an outlier is now made as above and thenanotube sample similarly extracted. In the case of an adhesiverequiring a cure the appropriate conditions (e.g., UV light, heat,hardener etc.) must be provided to effect the cure prior to attemptingto extract the sample.

[0056] In this implementation, if electrical connection to the nanotubesample is required such connection can be guaranteed (despite the use ofinsulating adhesives) by applying the adhesive to only the very tip ofthe mounting device and selecting only the longest outliers to ensurethat there is direct contact between the uncoated, electricallyconducting portion of the mounting device tip (beyond the adhesivecovered portion) and the nanotube sample.

[0057] In some applications, the mounted nanotube sample may besubjected to mechanical or environmental stresses which make itdesirable to make the attachment to the mounting device more robust.This is accomplished by the application of a coating over the nanotubesample and mounting device tip. While this has been achieved by dippingthe assembly in a fluid solution of the coating material, it is foundthat delivery of the coating material from the vapor phase has severaldistinct advantages. These include: a) stresses on the sample areminimized during the process ensuring that the sample survives, b) theamount of the coating material applied may be controlled by samplecontrol over the time of deposition and is not subject to more difficultto control viscosity and surface tension parameters encountered in theapplication of fluid media, and c) for some coating materials (inparticular, those which do not undergo a liquid phase upon condensing onthe sample) it is possible to obtain a nanometer scale coating thicknesswhich is uniform over the whole of the nanotube sample.

[0058] Coatings applied in this way can include cyanoacrylate,methacrylate (modified and pure, both in two part cure formulation and aUV cure formulation), Parylene2 and polyimide. Other types of coatingsthat may be applied from the vapor phase include silicon from the UVdecomposition of silanes in an inert atmosphere as well as silicondioxide from the decomposition of silanes in an oxygen atmosphere.Finally, metals may be coated on the nanotube samples from vapors oforganometallic species (e.g., Fe from Fe(CO)_(g)).

[0059] In some applications, the coating has important utility beyondthat of securing the nanotube sample onto the mounting device tip. Inthe case of some biological and electrochemical probing applications, itis necessary that the probe be electrically insulated from its fluidenvironment at all but its very tip. The polymeric coatings mentionedabove each provide a uniform, insulating coating that adds littlethickness to the probe diameter, are ideal for this application. Thepolymer for coatings may include a florescent species for renderingnanotubes more visible, e.g., against the background of a cell. In otherapplications (e.g., for field emission sources) it is necessary thatthermal vibrations of the nanotube sample, fixed as it is at only oneend, be minimized. In such cases, the coating thickness may be made aslarge as necessary to adequately stabilize the tip. In both theseinstances, it may be necessary to remove the coating from the last fewhundred nanometers at the tip of the nanotube sample.

[0060] If the holder fixing the mounting element with its mountednanotube sample on stage A and the holder fixing an opposing sharptipped electrode on stage B are electrically isolated from themicroscope base, and each other, an electrical potential can be appliedbetween the nanotube sample and opposing electrode. A consequence ofthis is that as stage A is translated so as to bring the nanotube sampletip into the proximity of the electrode tip, the oppositely chargedobjects attract each other causing the flexible nanotube sample to bendinto alignment with the electrode tip. One utility of this involvesvisibility of the attached sample. It was mentioned above that for thintipped nanotube samples (single or thin bundle), the visibility of thesample depends strongly on the relative angles between the incidentlight, the nanotube axis, and the microscope optic axis. Thus, in anattempt to mount a nanotube sample, if the nanotube is not observed atthe tip of the mounting device it may in fact be attached there however,at an angle that does not permit its observation. By allowing theorientation of the nanotube to be modified to an angle allowing it to beobserved, this technique provides a quick assay of whether or not asample has been attached. The opposing electrode can simply be anotheroutlier from the layer of nanotubes from which mounting is beingattempted on stage B.

[0061] Probes for Analytical Applications

[0062] The molecular nanotubes attached to a mounting element, accordingto the present invention, enable the fabrication of probes for variousanalytical applications on a nanoscale. The probe and its mountingelement essentially provide a transducer for interacting with ananoscale environment. Conventional probe microscopy techniques areenabled and improved by the use of nanotube probe elements of thisinvention.

[0063] A molecular nanotube probe element is fundamentally differentfrom conventional probe microscopy tips in shape, and mechanical,electronic, chemical and electromagnetic properties. These differencespermit new modes of operation of probe microscopes, and new forms ofprobe microscopy.

[0064] Probes according to the present invention include those useful inimaging, at nanoscale resolution or greater, surfaces and othersubstrates including individual atoms or molecules such as biomolecules.Examples of conventional probe microscopy of this type include scanningtunneling microscopes (STM), atomic force microscopes (AFM), scanningforce microscopes (SFM), magnetic force microscopes (MFM), and magneticresonance force microscopes (MRFM). In this type of probe theconventional tip element can be replaced by the nanotube assembly andexisting mounting systems (e.g. the cantilever or a tip on a cantilever)form the mounting element.

[0065]FIG. 1e shows a typical STM or AFM probe having a cantilever 180which has a conventional tip 182 and a nanotube assembly 184 (in thiscase a single nanotube) extending from the tip. The nanotube assembly184 may be attached to the tip 182 in the sane fashion discussedearlier. The cantilever 180 can be used as a part of larger device inthe known manner. A coating, as described above, may be applied to theprobe and the mounting element.

[0066] In a preferred embodiment, the mounting devices may be pre-coatedwith a layer of conductive metal in order to produce a good electricalcontact to the nanotube probe.

[0067] When used in tapping mode AFM (where the change in amplitude ofan oscillating cantilever driven near its resonant frequency ismonitored as the tip taps the surface; the sharp frequency response ofhigh-quality cantilevers make this technique exquisitely sensitive. Acarbon nanotube tip, such as that shown in FIG. 1(c), has the unusualadvantage that it is both stiff below a certain threshold force, but iscompliant above that threshold force. The is no bending of the nanotubeat all when it encounters a surface at near normal incidence until theEuler buckling force, F_(EULER) is exceeded, which is given by theequation:

F _(EULER) =nπ ² YI/L ²  (1)

[0068] where n is a parameter determined by the tip mounting, Y is theYoung's modulus, I is the moment of inertia of the tip cross section andL is the free length of the tip extending beyond the mounting assembly.The Euler buckling force for tips of the preferred embodiment describedabove is in the one nano-Newton range. Once the Euler bucking force isexceeded, the nanotube will bend easily through large amplitudes withlittle additional force. Euler buckling therefore serves as a kind ofinsurance policy during SFM imaging: the maximum force that can betransmitted to the sample is F_(EULER). In addition, the nanotube tip isextremely gentle when touching an object laterally. The bending motionfor side-directed forces is harmonic with a force constant,k_(n)=3YI/L³. For the nanotube tip of FIG. 1(c), k_(n=)6.3 pN/nm.

[0069] The mechanism for reduction in the tapping amplitude in operationis almost entirely elastic. The spring force from the bending nanotubeproduces a de-excitation of the cantilever oscillation at drivingfrequencies below the critical frequency, ω°. The result is that gentle,reliable AFM imaging may be accomplished in the tapping mode with evenextremely stiff, high-resonant frequency cantilevers. In contrast to thehard silicon pyramidal tip which can easily generate impact forces >100nN per tap which may substantially modify the geometry of “soft” samplessuch as large bio-molecules. The nanotube probe serves as a compliantspring which moderates the impact of each tap on the surface, the peakforce never exceeding F_(EULER).

[0070] An example of a typical nanotube probe according to oneembodiment of the invention is shown in FIGS. 2a-c. A single nanotubewas attached to the pyramidal tip of a silicon cantilever for scanningforce microscopy. The majority of the 5.5 micron length extending beyondthe pyramidal silicon tip was a bundle of 5-10 parallel nanotubes,arranged in van der Waals contact along their length. As evident in theTEM image of FIG. 2c, this bundle narrows down to just a single nanotube5 nm in diameter, extending alone for the final 250 nm.

[0071] The nanotube tip shown in FIGS. 2a-c was operated in tapping modeSFM. FIG. 3a shows the frequency dependence of the amplitude of thecantilever as it engaged a freshly cleaved surface of mica in air. Asseen in the inset, the tapping amplitude when the cantilever was drivennear its resonant frequency (253.8 kHz) dropped rapidly as soon as thenanotube tip came in contact with the mica surface. The amplitudedropped to near zero when the nanotube hit the surface at the midpointof its oscillation, and then recovered to nearly the full in-airamplitude when the surface was so close that the tip was always incontact, with the nanotube flexing throughout the oscillation. FIG. 3bshows the result of a direct numerical simulation of this experimentusing the buckling force expression of equation (1). The sharpness ofthe recovery of oscillation amplitude near the critical frequency, ω°254.2 kHz is a sensitive function of the buckling force.

[0072] Referring to FIGS. 4a-d, which show that long, narrow nanotubetips can reach into deep trenches previously inaccessible to highresolution scanning probes. As is evident in FIG. 4a, the normalpyramidal tip is simply too wide to reach the bottom of a 0.4 m wide 0.8m deep trench, while the nanotube permits the roughness of the siliconsurface at the bottom to be imaged easily. Also as shown in FIG. 4d, itis possible using a voltage pulse on the nanotube to deposit a 40 nm dotof carbon at the bottom of the trench, and then to go back and image thedot. Due to the “spring loading” of the nanotube bundle to thecantilever and the high strength and flexibility of the carbonnanotubes, SFM imaging of tortuous structures such as the trenches shownin FIGS. 4a-d can be done without fear of damage either to the nanotubetip or the trench structure itself.

[0073] One of the principal limits in SFM imaging in air has been thatat normal humidity the surface is covered with layer of water, and thecapillary adhesion forces produced when the tip makes contact aretypically 10-100 nN. As a result one is forced to use high forceconstant cantilevers oscillating with substantial amplitude to insurethat the tip does not get caught by the surface. Due to the smalldiameter of the nanotube, the capillary adhesion force of nanotube tipsis generally reduced to <5 nN and often as low as 0.05 nN, permittingtapping mode imaging with cantilevers having force constants as small as0.01 N/m at a peak-to-peak amplitude of 10 nm.

[0074] In order to get away entirely from the capillary adhesion forceit is now conventional to place the entire AFM transducer assembly undersome fluid—normally water. However, now that the cantilever mustoscillate in water it is no longer possible to operate at high frequencyand high Q. A nanotube tip similar to that of FIG. 2a, was immersedunder the surface of water, thus leaving the cantilever free tooscillate in air. FIG. 5a shows that the frequency dependence of thecantilever oscillation is only slightly affected when the lower 0.7micrometer length of the nanotube is immersed in water within thetrench. Also shown is the amplitude of the cantilever oscillation as afunction of distance from the meniscus at the top of the trench. FIGS.5b and c show the amplitude change upon dipping a nanotube probe intothe flooded trench. The first contact with the water surface occurred atz=0. The nanotube tip encountered the bottom of the trench at z=−820 nm.The trace in FIG. 5b was done at the resonant frequency of thecantilever oscillating in air (234.74 kHz), and the trace in FIG. 5e wasdone at 235.65 kHz ,where the oscillation amplitude is seen tosubstantially increase when the tip of the nanotube extends under thewater surface.

[0075] Since the nanotubes can be electrically conducive, they may beused as probes for scanning tunneling microscopy, STM, and in variousscanning electrochemical modes as well. FIG. 6 shows an example ofatomic-scale resolution STM using a carbon nanotube to image the chargedensity waves on a freshly cleaved 1T-TaS₂ surface.

[0076] The nanotube probe assemblies of this invention also enable theelicitation of other information from and/or about nanoscale objects orat nanoscale resolution such as conventional friction force microscopy(FFM) which measures the atomic scale friction of a surface by observingthe transverse deflection of a cantilever mounted probe tip. Thecompliance of a nanotube probe of the present invention above the Eulerthreshold as described above, provides for a totally new method ofelastic force microscopy (EFM). By calibration of the Euler bucklingforce for an individual probe tip, and making appropriate AFMmeasurements with that tip, one can obtain direct information about theelastic properties of the object being imaged.

[0077] Probe tips may also be used to perform nanoscale surfacetopography measurement. The vertical and horizontal motions of the probeassembly can be calibrated by measurement of surfaces having knowngeometries (e.g., pyrolytic graphite with surface steps). Athusly-calibrated probe assembly can provide precise me of thetopography of surfaces and fabricated elements such as vias and trencheson integrated-circuit elements in silicon, gallium arsenide, and otherelectronic substrates.

[0078] A number of other new probe microscopy techniques for obtaininginformation at nanoscale resolution or about/from nanoscale objects isenabled by the present invention. For example, mechanical resonancemicroscopy (MRM) can be facilitated by mechanical resonances in thenanotube probe element itself. These resonances may be utilized as ameans of transduction of information about the object being sensed ormodified. Such resonances, as will be known by one skilled in the artcan be sensed by optical, piezoelectric, magnetic and/or electronicmeans. Interaction of a mechanically resonant probe tip with otherobjects may be facilitated by derivitization of the probe tip orinclusion of an endohedral species (e.g., one which is optically- ormagnetically-active) at or near the probe tip. Mechanically resonanttips can be employed to deliver or receive electronic or optical signalsbetween electronic or optical circuits.

[0079] Another novel method for transducing information about an objectbeing sensed or modified is based on the property of the nanotube probeassemblies of this invention to act as sensitive “antenna” forelectromagnetic radiation (particularly at optical frequencies). Theprobe's response to electromagnetic radiation may be sensed byscattering of that radiation by the probe itself detection andmeasurement of radio frequency (RF) or microwave frequency (MW) currentspassing through the probe as it and the object being sensed interacttogether in a nonlinear way with electromagnetic radiation of two ormore frequencies. Moreover, via its interaction with electromagneticfields of specified frequencies, the probe may excite electronic,atomic, molecular or condensed-matter states in the object beingexamined, and the transduction of information about that object mayoccur by observation of the manifestations of these states.

[0080] In another embodiment, the devices of the present invention canfacilitate the storing of information in nanoscale objects and theretrieval of the stored information from those objects by virtue of theelectronic, mechanical, physical an/or optical response of the molecularnanotube probe elements in interaction with said objects.

[0081] Of particular interest is the use of molecular nanotube probedevices according to the present invention in biological systems. In onesuch application, DNA sequencing can be performed, for example, by AFMimaging of DNA molecules with a nanotube probe element that, due to itsphysical and chemical properties, permits the recognition of individualbases in the molecule. In another biological application, the probes mayalso be used as nanelectrodes for electrochemical studies of livingcells. In another embodiment, an ion-selective nanotube may befabricated from a open nanotube filled with water and covered with aselective membrane (e.g., ion-exchange resin, or even a biologicalmembrane). This nanoelectrode can monitor specific cytoplasmic ions witha spatial resolution far superior to those presently available. In apreferred embodiment, a calcium-specific nanoelectrode may be used toprovide high spatial and temporal resolution in the measurement ofchanges in the cytosolic calcium concentrations, often the response tostimuli, in various types of cells.

[0082] Derivatized probes can serve as sensors or sensor arrays thateffect selective binding to substrates. Devices such as these can beemployed for rapid molecular-level screening assays for pharmaceuticalsand other bioactive materials.

[0083] Probes As Nanoactuators

[0084] The molecular nanotube probe elements of the present inventioncan also be employed to effect manipulation or modification of objectson a nanoscale to facilitate the fabrication of nanotechnology devicesor elements. In general, these techniques employ some form of tip/sampleinteraction to effect this manipulation or modification. Thisinteraction can be direct physical interaction (e.g., to push, pull ordrag atoms, molecules, or small objects to a specified location).Indirect interaction can be supplied through forces such as repulsion orattraction (atomic force or magnetic force). Emission from the nanotubetip (e.g. electrons, photons, magnetic forces and the like) may alsoeffect the interaction by electromechanical or chemical means, asdescribed more fully below.

[0085] Probe-like assemblies of molecular nanotubes can be used with orwithout derivatives as tools to effect material handling and fabricationof nanoscale devices. Examples of nanostructure fabrication are given inU.S. Pat. No. 5,126,574 to Gallagher and in U.S. Pat. No. 5,521,390 toSato et al., both incorporated by reference in their entireties.

[0086] The nanoscale device of the present invention also may be usedfor nanolithography. A nanotube may be mounted on the tip of a device,such as a STM. In operation, the STM tip then produces ahighly-localized beam of electrons which may be used to expose anelectron-sensitive resist or to directly modify the surface upon whichit impinges. Such surface modification or exposure of a resist is usefulin fabrication of electronic and other devices having dimensions in thenanometer range, which are smaller than those now available.

[0087] Addition of selected chemical species to the end of the nanotubeprobe tip permits the probe tip to participate in specific chemical orelectrochemical processes. The tip can then act as an agent for chemicalmodification of a surface or object on a nanometer scale. The pattern ofthis chemical modification is controlled by the collective action of theprobe tip and its mounting mechanism.

[0088] The ability to precisely and reproducibly covalently bond achemical moiety at the tip of the preferred carbon nanotube probestructure facilitates another form of chemical interaction with asurface that results in a powerful nanofabrication technique. The(10,10) armchair carbon nanotube has, at its tip, a single pentagon withreactive sites for addition chemistry in its radiating double bonds. Bydipping a probe (or array of probes) into a reactive medium, preferablya solution, it is possible to add a chemical moiety that acts as acatalyst to the nanotube tip. This moiety can be a catalyst per se(e.g., an enzyme) or a linking moiety (e.g., a co-enzyme) that has anaffinity for a second moiety that is the catalytic moiety, which can beadded in a second step. The preferred system only creates a chemicalreaction product when the catalyst containing probe tip, the substratesurface, and a reagent(s) flowing over the substrate come into contact.An element formed by the catalyzed reaction product can be positioneddiscreetly or continuously by intermittent or continuous contact of theprobe tip with the surface of a substrate. A complex nanostructure canbe built up by performing the above-described probe/surface reactionstep sequentially with different probe catalyst/reagent systems todeposit different pattern elements of the device being nanofabricated.Confirmation that the reaction product elements have in fact been formedon the surface can be accomplished by employing a phosphorescent markerthat is formed upon completion of the reaction. This system can producea composite structure with extremely fine lines as well as elements ofdiffering shape and composition. The reaction products forming thepattern(s) or device structure can be biomolecules, which facilitate thefabrication of nanoscale biostructures that may mimic the function ofnatural biosystems.

[0089] Nanotube probes or probe arrays with attached therapeuticmoieties can also be used in cell-based therapies to inject thesetherapeutic moieties directly into cells where they are needed. Releaseof bound moieties can be effected, for example, by a voltage pulse orother bond destabilizing signal. The nanotube probes of the presentinvention can also be employed to deliver genetic material (i.e., DNA)attached to the probe tip to cells by similar injection techniques(e.g., during embryonic development).

[0090] A nanotube mounted on a STM tip may also be used in desorptioninduced by electronic transitions, or DIET. Field emitted electrons fromthe STM tip may be used to bring about hydrogen desorption, giving riseto uses such as nanolithography and material modification on thenanometer and even on the atomic scale.

[0091] A STM-tip attached nanotube may also be used inchemically-assisted field evaporation/desorption (CAFE). The accuracy ofthe nanotube provides the ability to access a particular location on asurface, break strong chemical bonds, transfer one atom or cluster ofatoms to the nanotube, and possibly redeposit the atom(s) at anotherlocation. Other interactions are also possible.

[0092] The nanotubes may also be used with scanned probe microscopy(SPM) to fabricate nanodevices. By attaching a nanotube to a tip of aSPM, a highly localized enhanced oxidation of a substrate can beachieved, and this may be used as an etch mark to create freestandingsilicon nanowires. By further processing the nanowire, other confinedstructures may also be produced.

[0093] Manipulators, or “nanotools,” may be embodied by devices of thepresent invention. It is possible to create “nanoforcepts” which,through motion of one or more nanotube probe tips, can grip and move anobject of nanometer dimensions. Specific chemical derivitization of theprobe end in this application can enhance, modify, or make chemicallyspecific the gripping action of the tip. Through electrical orelectrochemical action, the tip can etch an object, moving atoms ormolecules in controlled patterns on a nanometer scale. Through catalyticcation of an individual tip or catalytic action of chemical groupsattached to the tip, one can achieve chemical modification of an objectwhich can be carried out in a pattern which serves to fabricate patternsor other nanometer scale objects. Direct fabrication of individualstructures on an atom-by-atom or molecule-by-molecule basis is possibleusing the nanoprobes disclosed in this invention. These nanotools may beused to manipulate other nanoobjects, and may also be used to fabricateMEMS (Micro Electro Mechanical Systems).

[0094] The following sections provide more detail on the preparation ofcarbon nanotubes for use in the devices of the present invention.

[0095] Carbon Nanotubes

[0096] Fullerenes are molecules composed entirely of sp²-hybridizedcarbons, arranged in hexagons and pentagons. Fullerenes (e.g., C₆₀) werefirst identified as closed spheroidal cages produced by condensationfrom vaporized carbon.

[0097] Fullerene tubes are produced in carbon deposits on the cathode incarbon arc methods of producing spheroidal fullerenes from vaporizedcarbon. Fullerene tubes may be closed at one or both ends with end capsor open at one or both ends. Ebbesen et al. (Ebbesen I), “Large-ScaleSynthesis Of Carbon Nanotubes,” Nature, Vol. 358, p. 220 (Jul. 16, 1992)and Ebbesen et al., (Ebbesen II), “Carbon Nanotubes,” Annual Review ofMaterial Science, Vol. 24, p. 235 (1994). Such tubes are referred toherein as carbon nanotubes. Many of the carbon nanotubes made by theseprocesses were multi-wall nanotubes, i.e., the carbon nanotubesresembled concentric cylinders. Carbon nanotubes having up to sevenwalls have been described in the prior art. Ebbesen II; Iijima et al.,“Helical Microtubules Of Graphitic Carbon,” Nature, Vol. 354, p. 56(Nov. 7, 1991).

[0098] Single-wall carbon nanotubes have been made in a DC arc dischargeapparatus of the type used in fullerene production by simultaneouslyevaporating carbon and a small percentage of Group VIII transition metalfrom the anode of the arc discharge apparatus. See Iijima et al.,“Single-Shell Carbon Nanotubes of 1 nm Diameter,” Nature, Vol. 363, p.603 (1993); Bethune et al., “Cobalt Catalyzed Growth of Carbon Nanotubeswith Single Atomic Layer Walls,” Nature, Vol. 63, p. 605 (1993); Ajayanet al., “Growth Morphologies During Cobalt Catalyzed Single-Shell CarbonNanotube Synthesis,” Chem. Phys. Lett., Vol. 215, p. 509 (1993); Zhou etal., “Single-Walled Carbon Nanotubes Growing Radially From YC₂Particles,” Appi. Phys. Lett, Vol. 65, p. 1593 (1994); Seraphin et al.,“Single-Walled Tubes and Encapsulation of Nanocrystals Into CarbonClusters,” Electrochem. Soc., Vol. 142, p. 290 (1995); Saito et al.,“Carbon Nanocapsules Encaging Metals and Carbides,” J. Phys. Chem.Solids, Vol. 54, p. 1849 (1993); Saito et al., “Extrusion of Single-WallCarbon Nanotubes Via Formation of Small Particles Condensed Near anEvaporation Source,” Chem. Phys. Lett., Vol. 236, p. 419 (1995). It isalso known that the use of mixtures of such transition metals cansignificantly enhance the yield of single-wall carbon nanotubes in thearc discharge apparatus. See Lambert et al., “Improving ConditionsToward Isolating Single-Shell Carbon Nanotubes,” Chem. Phys. Lett., Vol.226, p. 364 (1994).

[0099] An improved method of producing single-wall nanotubes isdescribed in U.S. Ser. No. 08/687,665, entitled “Ropes of Single-WalledCarbon Nanotubes” incorporated herein by reference in its entirety. Thismethod uses, inter alia, laser vaporization of a graphite substratedoped with transition metal atoms, preferably nickel, cobalt, or amixture thereof to produce single-wall carbon nanotubes in yields of atleast 50% of the condensed carbon. The single-wall nanotubes produced bythis method tend to be formed in clusters, termed “ropes,” of 10 to 1000single-wall carbon nanotubes in parallel alignment, held together by vander Waals forces in a triangular lattice.

[0100] The single wall tubular fullerenes are distinguished from eachother by double index (n,m) where n and m are integers that describe howto cut a single strip of hexagonal “chicken-wire” graphite so that itmakes the tube perfectly when it is wrapped onto the surface of acylinder and the edges are sealed together. When the two indices are thesame, m=n, the resultant tube is said to be of the “arm-chair” (or n,n)type, since when the tube is cut perpendicular to the tube axis, onlythe sides of the hexagons are exposed and their pattern around theperiphery of the tube edge resembles the arm and seat of an arm chairrepeated n times. Arm-chair tubes are a preferred form of single-wallcarbon nanotubes since they are metallic, and have extremely highelectrical and thermal conductivity. In addition, all single-wallnanotubes have extremely high tensile strength.

[0101] Purification of Single-Wall Nanotubes

[0102] The product of a typical process for making mixtures containingsingle-wall carbon nanotubes is a tangled felt which can includedeposits of amorphous carbon, graphite, metal compounds (e.g., oxides),spherical fullerenes, catalyst particles (often coated with carbon orfullerenes) and possibly multi-wall carbon nanotubes. The single-wallcarbon nanotubes may be aggregated in “ropes” or bundles of essentiallyparallel nanotubes.

[0103] When material having a high proportion of single-wall nanotubesis purified as described herein, the preparation produced will beenriched in single-wall nanotubes, so that the single-wall nanotubes aresubstantially free of other material. In particular, single-wallnanotubes will make up at least 80% of the preparation, preferably atleast 90%, more preferably at lest 95% and most preferably over 99% ofthe material in the purified preparation.

[0104] One preferred purification process comprises heating theSWNT-containing felt under oxidizing conditions to remove the amorphouscarbon deposits and other contaminating materials. In a preferred modeof this purification procedure, the felt is heated in an aqueoussolution of an inorganic oxidant, such as nitric acid, a mixture ofhydrogen peroxide and sulfuric acid, or potassium permanganate.Preferably, SWNT-containing felts are refluxed in an aqueous solution ofan oxidizing acid at a concentration high enough to etch away amorphouscarbon deposits within a practical time frame, but not so high that thesingle-wall carbon nanotube material will be etched to a significantdegree. Nitric acid at concentrations from 2.0 to 2.6 M have been foundto be suitable. At atmospheric pressure, the reflux temperature of suchan aqueous acid solution is about 101-102° C.

[0105] In a preferred process, the nanotube-containing felts can berefluxed in a nitric acid solution at a concentration of 2.6 M for 24hours. Purified nanotubes may be recovered from the oxidizing acid byfiltration through, e.g., a 5 micron pore size TEFLON filter, likeMillipore Type LS. Preferably, a second 24 hour period of refluxing in afresh nitric solution of the same concentration is employed followed byfiltration as described above.

[0106] Refluxing under acidic oxidizing conditions may result in theesterification of some of the nanotubes, or nanotube contaminants. Thecontaminating ester material may be removed by saponification, forexample, by using a saturated sodium hydroxide solution in ethanol atroom temperature for 12 hours. Other conditions suitable forsaponification of any ester linked polymers produced in the oxidizingacid treatment will be readily apparent to those skilled in the art.Typically the nanotube preparation will be neutralized after thesaponification step. Refluxing the nanotubes in 6 M aqueous hydrochloricacid for 12 hours has been found to be suitable for neutralization,although other suitable conditions will be apparent to the skilledartisan.

[0107] After oxidation, and optionally saponification andneutralization, the purified nanotubes may be collected by settling orfiltration preferably in the form of a thin mat of purified fibers madeof ropes or bundles of SWNTs, referred to hereinafter as “bucky paper”.In a typical example, filtration of the purified and neutralizednanotubes on a TEFLON membrane with 5 micron pore size produced a blackmat of purified nanotubes about 100 microns thick. The nanotubes in thebucky paper may be of varying lengths and may consists of individualnanotubes, or bundles or ropes of up to 10³ single-wall nanotubes, ormixtures of individual single-wail nanotubes and ropes of variousthicknesses. Alternatively, bucky paper may be made up of nanotubeswhich are homogeneous in length or diameter and/or molecular structuredue to fractionation as described hereinafter.

[0108] The purified nanotubes or bucky paper are finally dried, forexample, by baking at 850° C. in a hydrogen gas atmosphere, to producedry, purified nanotube preparations.

[0109] When laser-produced single-wall nanotube material, produced bythe two-laser method of U.S. Ser. No.08/687,665, was subjected refluxingin 2.6 M aqueous nitric acid, with one solvent exchange, followed bysonication in saturated NaOH in ethanol at room temperature for 12hours, then neutralization by refluxing in 6 M aqueous HCl for 12 hours,removal from the aqueous medium and baking in a hydrogen gas atmosphereat 850 C. in 1 atm H₂ gas (flowing at 1-10 sccm through a 1″ quartztube) for 2 hours, detailed TEM, SEM and Raman spectral examinationshowed it to be >99% pure, with the dominant impurity being a fewcarbon-encapsulated Ni/Co particles. (See FIGS. 7A, 7B, and 7C).

[0110] In another embodiment, a slightly basic solution (e.g., pH ofapproximately 8-12) may also be used in the saponification step. Theinitial cleaning in 2.6 M HNO₃ converts amorphous carbon in the rawmaterial to various sizes of linked polycyclic compounds, such as fulvicand humic acids, as well as larger polycyclic aromatics with variousfunctional groups around the periphery, especially the carboxylic acidgroups. The base solution ionizes most of the polycyclic compounds,making them more soluble in aqueous solution. In a preferred process,the nanotube containing felts are refluxed in 2-5 M HNO₃ for 6-15 hoursat approximately 110°-125° C. Purified nanotubes may be filtered andwashed with 10 mM NaOH solution on a 3 micron pore size TSTP Isoporefilter. Next, the filtered nanotubes polished by stirring them for 30minutes at 60° C. in a S/N (Sulfuric acid/Nitric acid) solution. In apreferred embodiment, this is a 3:1 by volume mixture of concentratedsulfuric acid and nitric acid. This step removes essentially all theremaining material from the tubes that is produced during the nitricacid treatment.

[0111] Once the polishing is complete, a four-fold dilution in water ismade, and the nanotubes are again fileted on the 3 micron pore size TSTPIsopore filter. The nanotubes are again washed with a 10 mM NaOHsolution. Finally, the nanotubes are stored in water, because drying thenanotubes makes it difficult to resuspend them.

[0112] Cutting Singe-Wall Carbon Nanotubes

[0113] Single-wall carbon nanotube produced by prior methods are so longand tangled that it is very difficult to purify them, or to manipulatethem. They can be cut into short enough lengths that they are no longertangled and the open ends annealed closed. The short, closed tubularcarbon molecules may be purified and sorted very readily usingtechniques that are similar to those used to sort DNA or size polymers.

[0114] Preparation of homogeneous populations of short carbon nanotubesmolecules may be accomplished by cutting and annealing (reclosing) thenanotube pieces followed by fractionation. The cutting and annealingprocesses may be carried out on a purified nanotube bucky paper, onfelts prior to purification of nanotubes or on any material thatcontains single-wall nanotubes. When the cutting and annealing processis performed on felts, it is preferably followed by oxidativepurification, and optionally saponification, to remove amorphous carbon.Preferably, the starting material for the cutting process is purifiedsingle-wall nanotubes, substantially free of other material.

[0115] The short nanotube pieces can be cut to a length or selected froma range of lengths, that facilitates their intended use. The length canbe from just greater than the diameter of the tube up to about 1,000times the diameter of the tube. Typical tubular molecules will be in therange of from about 5 to 1,000 nanometers or longer. For making templatearrays useful in growing carbon fibers of SWNT as described below,lengths of from about 50 to 500 nm are preferred.

[0116] Any method of cutting that achieves the desired length ofnanotube molecules without substantially affecting the structure of theremaining pieces can be employed. The preferred cutting method employsirradiation with high mass ions. In this method, a sample is subjectedto a fast ion beam, e.g., from a cyclotron, at energies of from about0.1 to 10 giga-electron volts. Suitable high mass ions include thoseover about 150 AMU's such as bismuth, gold, uranium and the like.

[0117] Preferably, populations of individual single-wall nanotubemolecules having homogeneous length are prepared staring with aheterogeneous bucky paper and cutting the nanotubes in the paper using agold (Au⁺³³) fast ion beam. In a typical procedure, the bucky paper(about 100 micron thick) is exposed to ^(˜)10¹² fast ions per cm², whichproduces severely damaged nanotubes in the paper, on average every 100nanometers along the length of the nanotubes. The fast ions createdamage to the bucky paper in a manner analogous to shooting 10-100 nmdiameter “bullet holes” through the sample. The damaged nanotubes thencan be annealed (closed) by heat sealing of the tubes at the point whereion damage occurred, thus producing a multiplicity of shorter nanotubemolecules. At these flux levels, the shorter tubular molecules producedwill have a random distribution of cut sizes with a length peak nearabout 100 nm. Suitable annealing conditions are well know in thefullerene art, such as for example, baking the tubes in vacuum or inertgas at 1200° C. for 1 hour.

[0118] The SWNTs may also be cut into shorter tubular molecules byintentionally incorporating defect-producing atoms into the structure ofthe SWNT during production. These defects can be exploited chemically(e.g., oxidatively attacked) to cut the SWNT into smaller pieces. Forexample, incorporation of 1 boron atom for every 1000 carbon atoms inthe original carbon vapor source can produce SWNTs with built-in weakspots for chemical attack.

[0119] Cutting may also be achieved by sonicating a suspension of SWNTsin a suitable medium such as liquid or molten hydrocarbons. One suchpreferred liquid is 1,2-dichloreothane. Any apparatus that producessuitable acoustic energy can be employed. One such apparatus is theCompact Cleaner (One Pint) manufactured by Cole-Parmer, Inc. This modeloperates at 40 KHZ and has an output of 20 W. The sonication cuttingprocess should be continued at a sufficient energy input and for asufficient time to substantially reduce the lengths of tubes, ropes orcables present in the original suspension. Typically times of from about10 minutes to about 24 hours can be employed depending on the nature ofthe starting material and degree of length reduction sought.

[0120] In another embodiment, sonification may be used to create defectsalong the rope lengths, either by the high temperatures and pressurescreated in bubble collapse (−5000° C. and −1000 atm), or by the attackof free radicals produced by sonochemistry. These defects are attackedby S/N to cleanly cut the nanotube, exposing the tubes underneath formore damage and cutting. In a preferred process, the nanotubes are bathsonocated while being stirred in 40-45° C. S/N for 24 hours. Next, thenanotubes are stirred with no sonification in the S/N for 2 hours at40-45° C. This is to attack, with the S/N, all the defects created bythe sonification without creating more defects. Then, the nanotubes arediluted four-fold with water, and then filtered using a 0.1 micron poresize VCTP filter. Next, the nanotubes are filtered and washed with a 10mM NaOH solution on the VCTP filter. The nanotubes are polished bystirring them for 30 minutes at 70° C. in a S/N solution. The polishednanotubes are diluted four-fold with water, filtered using the 0.1micron pore size VCTP filters, then filtered and washed with 10 mM NaOHon a 0.1 micron pore size VCTP filter, and then stored in water.

[0121] Oxidative etching (e.g., with highly concentrated nitric acid)can also be employed to effect cutting of SWNTs into shorter lengths.For example, refluxing SWNT material in concentrated HNO₃ for periods ofseveral hours to 1 or 2 days will result in significantly shorter SWNTs.The rate of cutting by this mechanism is dependent on the degree ofhelicity of the tubes. This fact may be utilized to facilitateseparation of tubes by type, i.e., (n,n) from (m,n).

[0122] In another embodiment, SWNTs can be cut using electron beamcutting apparatus in the known manner. Nanotubes may also be cut by theuse of a plasma arc. Combination of the foregoing cutting techniques canalso be employed.

[0123] Homogeneous populations of single-walled nanotubes may beprepared by fractionating heterogeneous nanotube populations afterannealing. The annealed nanotubes may be disbursed in an aqueousdetergent solution or an organic solvent for the fractionation.Preferably the tubes will be disbursed by sonication in benzene,toluene, xylene or molten naphthalene. The primary function of thisprocedure is to separate nanotubes that are held together in the form ofropes or mats by van der Waals forces. Following separation intoindividual nanotubes, the nanotubes may be fractionated by size by usingfractionation procedures which are well known, such as procedures forfractionating DNA or polymer fractionation procedures. Fractionationalso can be performed on tubes before annealing, particularly if theopen ends have substituents (carboxy, hydroxy, etc.), that facilitatethe fractionation either by size or by type. Alternatively, the closedtubes can be opened and derivatized to provide such substituents. Closedtubes can also be derivatized to facilitate fractionation, for example,by adding solubilizing moieties to the end caps.

[0124] Electrophoresis is one such technique well suited tofractionation of SWNT molecules since they can easily be negativelycharged. It is also possible to take advantage of the differentpolarization and electrical properties of SWNTs having differentstructure types (e.g., arm chair and zig-zag) to separate the nanotubesby type. Separation by type can also be facilitated by derivatizing themixture of molecules with a moiety that preferentially bonds to one typeof structure.

[0125] In a typical example, a 100 micron thick mat of black buckypaper, made of nanotubes purified by refluxing in nitric acid for 48hours was exposed for 100 minutes to a 2 GeV beam of gold (Au⁺³³) ionsin the Texas A&M Superconducting Cyclotron Facility (net flux of up to10¹² ions per cm²). The irradiated paper was baked in a vacuum at 1200°C. for 1 hr to seal off the tubes at the “bullet holes”, and thendispersed in toluene while sonicating. The resultant tubular moleculeswere examined via SEM, AFM and TEM.

[0126] The procedures described herein produce tubular molecules thatare single-wall nanotubes in which the cylindrical portion is formedfrom a substantially defect-free sheet of graphene (carbon in the formof attached hexagons) rolled up and joined at the two edges parallel toits long axis. The nanotube can have a fullerene cap (e.g., hemispheric)at one end of the cylinder and a similar fullerene cap at the other end.One or both ends can also be open. Prepared as described herein, theseSWNT molecules are substantially free of amorphous carbon. Thesepurified nanotubes are effectively a whole new class of tubularmolecules.

[0127] In general the length, diameter and helicity of these moleculescan be controlled to any desired value. Preferred lengths are up to 10⁶hexagons; preferred diameters are about 5 to 50 hexagon circumference;and the preferred helical angle is 0° to 30°.

[0128] Preferably, the tubular molecules are produced by cutting andannealing nanotubes of predominately arm-chair (n,n) configuration,which may be obtained by purifying material produced according to themethods of U.S. Ser. No. 08/687,665. These (n,n) carbon molecules,purified as described herein, are the first truly “metallic molecules.”The metallic carbon molecules are useful as probes for scanning probemicroscopy such as are used in scanning tunneling microscopes (STM) andatomic force microscopes (AFM).

[0129] Derivitization of Carbon Nanotubes

[0130] The tubular carbon molecules (including the multiwall forms)produced as described above can be chemically derivatized at their ends(which may be made either open or closed with a hemi-fullerene dome).Derivatization at the fullerene cap structures is facilitated by thewell-known reactivity of these structures. See, “The Chemistry ofFullerenes” R. Taylor ed., Vol. 4 of the advanced Series in Fullerenes,World Scientific Publishers, Singapore, 1995; A. Hirsch, “The Chemistryof the Fullerenes,” Thieme, 1994. Alternatively, the fullerene caps ofthe single-walled nanotubes may be removed at one or both ends of thetubes by short exposure to oxidizing conditions (e.g., with nitric acidor O₂/CO₂) sufficient to open the tubes but not etch them back too far,and the resulting open tube ends maybe derivatized using known reactionschemes for the reactive sites at the graphene sheet edge.

[0131] In general, the structure of such molecules can be shown asfollows:

[0132] where

[0133] is a substantially defect-free cylindrical graphene sheet (whichoptionally can be doped with non-carbon atoms) having from about 10² toabout 10⁶ carbon atoms, and having a length of from about 5 to about1000 nm, preferably about 5 to about 500 nm;

[0134] is a fullerene cap that fits perfectly on the cylindricalgraphene sheet, has at least six pentagons and the remainder hexagonsand typically has at least about 30 carbon atoms;

[0135] n is a number from 0 to 30, preferably 0 to 12; and

[0136] R, R¹, R², R³, R⁴, and R⁵ each may be independently selected

[0137] from the group consisting of hydrogen; alkyl, acyl, aryl,aralkyl, halogen; substituted or unsubstituted thiol; unsubstituted orsubstituted amino; hydroxy, and OR′ wherein R′ is selected from thegroup consisting of hydrogen, alkyl, acyl, aryl aralkyl, unsubstitutedor substituted amino; substituted or unsubstituted thiol; and halogen;and a linear or cyclic carbon chain optionally interrupted with one ormore heteroatom, and optionally substituted with one or more ═O, or ═S,hydroxy, an aminoalkyl group, an amino acid, or a peptide of 2-8 aminoacids.

[0138] The following definitions are used herein.

[0139] The term “alkyl” as employed herein includes both straight andbranched chain radicals, for example methyl, ethyl, propyl, isopropyl,butyl, t-butyl, isobutyl, pentyl, hexyl, isohexyl, heptyl,4,4-dimethylpentyl, octyl, 2,2,4-trimethylpentyl, nonyl, decyl, undecyl,dodecyl, the various branched chain isomers thereof. The chain may belinear or cyclic, saturated or unsaturated, containing, for example,double and triple bonds. The alkyl chain may be interrupted orsubstituted with, for example, one or more halogen, oxygen, hydroxy,silyl, amino, or other acceptable substituents.

[0140] The term “acyl” as used herein refers to carbonyl groups of theformula —COR wherein R may be any suitable substituent such as, forexample, alkyl, aryl, aralkyl, halogen; substituted or unsubstitutedthiol; unsubstituted or substituted amino, unsubstituted or substitutedoxygen, hydroxy, or hydrogen.

[0141] The term “aryl” as employed herein refers to monocyclic, bicyclicor tricyclic aromatic groups containing from 6 to 14 carbons in the ringportion, such as phenyl, naphthyl substituted phenyl, or substitutednaphthyl, wherein the substituent on either the phenyl or naphthyl maybe for example C₁₋₄ alkyl, halogen, C₁₋₄alkoxy, hydroxy or nitro.

[0142] The term “aralkyl” as used herein refers to alkyl groups asdiscussed above having an aryl substituent, such as benzyl,p-nitrobenzyl, phenylethyl, diphenylmethyl, and triphenylmethyl.

[0143] The term “aromatic or non-aromatic ring” as used herein includes5-8 membered aromatic and non-aromatic rings uninterrupted orinterrupted with one or more heteroatom, for example O, S, SO, SO₂, andN, or the ring may be unsubstituted or substituted with, for example,halogen, alkyl, acyl, hydroxy, aryl, and amino, said heteroatom andsubstituent may also be substituted with, for example, alkyl, acyl,aryl, or aralkyl.

[0144] The term “linear or cyclic” when used herein includes, forexample, a linear chain which may optionally be interrupted by anaromatic or non-aromatic ring. Cyclic chain includes, for example, anaromatic or non-aromatic ring which may be connected to, for example, acarbon chain which either precedes or follows the ring.

[0145] The term “substituted amino” as used herein refers to an aminowhich may be substituted with one or more substituent, for example,alkyl, acyl, aryl, aralkyl, hydroxy, and hydrogen.

[0146] The term “substituted thiol” as used herein refers to a thiolwhich may be substituted with one or more substituent, for example,alkyl, acyl, aryl, aralkyl, hydroxy, and hydrogen.

[0147] Typically, open ends may contain up to about 20 substituents andclosed ends may contain up to about 30 substituents. It is preferred,due to stearic hindrance, to employ up to about 12 substituents per end.

[0148] In addition to the above described external derivatization, theSWNT molecules of the present invention can be modified endohedrally,i.e., by including one or more metal atoms inside the structure, as isknown in the endohedral fullerene art. It is also possible to “load” theSWNT molecule with one or more smaller molecules that do not bond to thestructures, e.g., C₆₀, to permit molecular switching as the C₆₀ buckyball shuttle back and forth inside the SWNT molecule under the influenceof eternal fields or forces.

[0149] To produce endohedral tubular carbon molecules, the internalspecies (e.g., metal atom, bucky ball molecules) can either beintroduced during the SWNT formation process or added after preparationof the tubular molecules. Incorporation of metals into the carbon sourcethat is evaporated to form the SWNT material is accomplished in themanner described in the prior art for making endohedralmetallofullerenes. Bucky balls, i.e., spheroidal fullerene molecules,are preferably loaded into the tubular carbon molecules of thisinvention by removing one or both end caps of the tubes employingoxidation etching described above, and adding an excess of bucky ballmolecules (e.g., C₆₀, C₇₀) by heating the mixture (e.g., from about 500to about 600° C.) in the presence of C₆₀ or C₇₀ containing vapor for anequilibration period (e.g., from about 12 to about 36 hours). Asignificant proportion (e.g., from a few tenths of a percent up to about50 percent or more) of the tubes will capture a bucky ball moleculeduring this treatment. By selecting the relative geometry of the tubeand ball this process can be facilitated. For example, C₆₀ and C₇₀ fitvery nicely in a tubular carbon molecule cut from a (10,10) SWNT (I.D.=1 nm). After the loading step, the tubes containing bucky ballmolecules can be closed (annealed shut) by heating under vacuum to about1100° C. Bucky ball encapsulation can be confirmed by microscopicexamination, e.g., by TEM.

[0150] Endohedrally loaded tubular carbon molecules can then beseparated from empty tubes and any remaining loading materials by takingadvantage of the new properties introduced into the loaded tubularmolecules, for example, where the metal atom imparts magnetic orparamagnetic properties to the tubes, or the bucky ball imparts extramass to the tubes. Separation and purification methods based on theseproperties and others will be readily apparent to those skilled in theart.

[0151] Fullerene molecules like C₆₀ or C₇₀ will remain inside theproperly selected tubular molecule (e.g., one based on (10,10) SWNTs)because from an electronic standpoint (e.g., by van der Waalsinteraction) the tube provides an environment with a more stable energyconfiguration than that available outside the tube.

[0152] Molecular Arrays of Singe-Wall Carbon Nanotubes

[0153] An application of particular interest for a homogeneouspopulation of SWNT molecules is production of a substantiallytwo-dimensional array made up of single-walled nanotubes aggregating(e.g., by van der Waals forces) in substantially parallel orientation toform a monolayer extending in directions substantially perpendicular tothe orientation of the individual nanotubes. Such monolayer arrays canbe formed by conventional techniques employing “self-assembledmonolayers” (SAM) or Langmiur-Blodgett films, see Hirch, pp. 75-76. Sucha molecular array is illustrated schematically in FIG. 8. In this Figurenanotubes 802 are bound to a substrate 804 having a reactive coating 806(e.g., gold).

[0154] Typically, SAMs are created on a substrate which can be a metal(such as gold, mercury or ITO (indium-tin-oxide)). The molecules ofinterest, here the SWNT molecules, are linked (usually covalently) tothe substrate through a linker moiety such as —S—, —S—(CH₂)_(n)—NH—,—SiO₃(CH₂)₃NH— or the like. The linker moiety may be bound first to thesubstrate layer or first to the SWNT molecule (at an open or closed end)to provide for reactive self-assembly. Langmiur-Blodgett films areformed at the interface between two phases, e.g., a hydrocarbon (e.g.,benzene or toluene) and water. Orientation in the film is achieved byemploying molecules or linkers that have hydrophilic and lipophilicmoieties at opposite ends.

[0155] The configuration of the SWNT molecular array may be homogenousor heterogeneous depending on the use to which it will be put. UsingSWNT molecules of the same type and structure provides a homogeneousarray of the type shown in FIG. 8. By using different SWNT molecules,either a random or ordered heterogeneous structure can be produced. Anexample of an ordered heterogeneous array is shown in FIG. 9 where tubes902 are (n,n), i.e., metallic in structure and tubes 904 are (m,n),i.e., insulating. This configuration can be achieved by employingsuccessive reactions after removal of previously masked areas of thereactive substrate.

[0156] One preferred use of the SWNT molecular arrays of the presentinvention is to provide a “seed” or template for growth of carbon fiberof single-wall carbon nanotubes as described below. The use of thistemplate is particularly useful for keeping the live (open) end of thenanotubes exposed to feedstock during growth of the fiber. The templatearray of this invention can be used as formed on the original substrate,cleaved from its original substrate and used with no substrate (the vander Waals forces will hold it together) or transferred to a secondsubstrate more suitable for the conditions of fiber growth.

[0157] Where the SWNT molecular array is to be used as a seed ortemplate for growing macroscopic carbon fiber as described below, thearray need not be formed as a substantially two-dimensional array. Anyform of array that presents at its upper surface a two-dimensional arraycan be employed. In the preferred embodiment, the template moleculararray is a manipulatable length of carbon fiber as produced below.

[0158] Another method for forming a suitable template molecular arrayinvolves employing purified bucky paper as the starting material. Uponoxidative treatment of the bucky paper surface (e.g., with O₂/CO₂ atabout 500° C.), the sides as well as ends of SWNTs are attacked and manytube and/or rope ends protrude up from the surface of the paper.Disposing the resulting bucky paper in an electric field (e.g., 100V/cm² results in the protruding tubes and or ropes aligning in adirection substantially perpendicular to the paper surface. These tubestend to coalesce due to van der Waals forces to form a molecular array.

[0159] Alternatively, a molecular array of SWNTs can be made by“combing” the purified bucky paper starting material. “Combing” involvesthe use of a sharp microscopic tip such as the silicon pyramid on thecantilever of a scanning force microscope (“SFM”) to align thenanotubes. Specifically, combing is the process whereby the tip of anSFM is systematically dipped into, dragged through, and raised up from asection of bucky paper. An entire segment of bucky paper could becombed, for example, by: (i) systematically dipping, dragging, raisingand moving forward an SFM tip along a section of the bucky paper, (ii)repeating the sequence in (i) until completion of a row; and (iii)repositioning the tip along another row and repeating (i) and (ii). In apreferred method of combing, the section of bucky paper of interest iscombed through as in steps (i)-(iii) above at a certain depth and thenthe entire process is repeated at another depth. For example, alithography script can be written and run which could draw twenty lineswith 0.5 μm spacing in a 10×10 μm square of bucky paper. The script canbe run seven times, changing the depth from zero to three μm in 0.5 μmincrements.

[0160] Growth of Carbon Fiber from SWNT Molecular Arrays

[0161] The present invention provides methods for growing carbon fiberfrom SWNT molecular arrays to any desired length. The carbon fiber whichcomprises an aggregation of substantially parallel carbon nanotubes maybe produced according to this invention by growth (elongation) of asuitable seed molecular array. The preferred SWNT molecular array isproduced as described above from a SAM of SWNT molecules ofsubstantially uniform length. The diameter of the fibers grown accordingto this method, which are useful in making nanoscale probes andmanipulators, can be any value from a few (<10) nanotubes to ropes up to10³ nanotubes.

[0162] The first step in the growth process is to open the growth end ofthe SWNTs in the molecular array. This can be accomplished as describedabove with an oxidative treatment. Next a transition metal catalyst isadded to the open-ended seed array. The transition metal catalyst can beany transition metal that will cause conversion of the carbon-containingfeedstock described below into highly mobile carbon radicals that canrearrange at the growing edge to the favored hexagon structure. Suitablematerials include transition metals, and particularly the Group VIIItransition metals, i.e., iron (Fe), cobalt (Co), nickel (NI), ruthenium(Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir) andplatinum (Pt). Metals from the lanthanide and actinide series andmolybdenum can also be used. Preferred are Fe, Ni, Co and mixturesthereof. Most preferred is a 50/50 mixture (by weight) of Ni and Co.

[0163] The catalyst should be present on the open SWNT ends as a metalcluster containing from about 10 metal atoms up to about 200 metal atoms(depending on the SWNT molecule diameter). Typically, the reactionproceeds most efficiently if the catalyst metal cluster sits on top ofthe open tube and does not bridge over more than one or two tubes.Preferred are metal clusters having a cross-section equal to from about0.5 to about 1.0 times the tube diameter (e.g., about 0.7 to 1.5 nm).

[0164] In the preferred process, the catalyst is formed, in situ, on theopen tube ends of the molecular array by a vacuum deposition process.Any suitable equipment, such as that used in Molecular Beam Epitaxy(MBE) deposition, can be employed. One such device is a Küdsen EffusionSource Evaporator. It is also possible to effect sufficient depositionof metal by simply heating a wire in the vicinity of the tube ends(e.g., a Ni/CO wire or separate Ni and CO wires) to a temperature belowthe melting point at which enough atoms evaporate from one wire surf(e.g., from about 900 to about 1300° C.). The deposition is preferablycarried out in a vacuum with prior outgassing. Vacuums of about 10⁻⁶ to10⁻⁸ Torr are suitable. The evaporation temperature should be highenough to evaporate the metal catalyst. Typically, temperatures in therange of 1500 to 2000° C. are suitable for the Ni/Co catalyst of thepreferred embodiment. In the evaporation process, the metal is typicallydeposited as monolayers of metal atoms. From about 1-10 monolayers willgenerally give the required amount of catalyst. The deposition oftransition metal clusters on the open tube tops can also be accomplishedby laser vaporization of metal targets in a catalyst deposition zone.

[0165] The actual catalyst metal cluster formation at the open tube endsis carried out by heating the tube ends to a temperature high enough toprovide sufficient species mobility to permit the metal atoms to findthe open ends and assemble into clusters, but not so high as to effectclosure of the tube ends. Typically, temperatures of up to about 500° C.are suitable. Temperatures in the range of about 400-500° C. arepreferred for the Ni/Co catalysts system of one preferred embodiment.

[0166] In a preferred embodiment, the catalyst metal cluster isdeposited on the open nanotube end by a docking process that insuresoptimum location for the subsequent growth reaction. In this process,the metal atoms are supplied as described above, but the conditions aremodified to provide reductive conditions, e.g., at 800° C., 10 millitorrof H₂ for 1 to 10 minutes. There conditions cause the metal atomclusters to migrate through the system in search of a reactive site.During the reductive heating the catalyst material will ultimately findand settle on the open tube ends and begin to etch back the tube. Thereduction period should be long enough for the catalyst particles tofind and begin to etch back the nanotubes, but not so long as tosubstantially etch away the tubes. By changing to the above-describedgrowth conditions, the etch-back process is reversed. At this point, thecatalyst particles are optimally located with respect to the tube endssince they already were catalytically active at those sites (albeit inthe reverse process).

[0167] The catalyst can also be supplied in the form of catalystprecursors which convert to active form under growth conditions such asoxides, other salts or ligand stabilized metal complexes. As an example,transition metal complexes with alkylamines (primary, secondary ortertiary) can be employed. Similar alkylamine complexes of transitionmetal oxides also can be employed.

[0168] In an alternative embodiment, the catalyst may be supplied aspreformed nanoparticles (i.e., a few nanometers in diameter) asdescribed in Dai et al., “Single-Wall Nanotubes Produced byMetal-Catalyzed Disproportionation of Carbon Monoxide,” Chem. Phys.Lett. 260 (1996), 471-475.

[0169] In the next step of the process, the SWNT molecular array withcatalyst deposited on the open tube ends is subjected to tube growth(extension) conditions. This may be in the same apparatus in which thecatalyst is deposited or a different apparatus. The apparatus forcarrying out this process will require, at a minimum, a source ofcarbon-containing feedstock and a means for maintaining the growing endof the continuous fiber at a growth and annealing temperature wherecarbon from the vapor can be added to the growing ends of the individualnanotubes under the direction of the transition metal catalyst.Typically, the apparatus will also have means for continuouslycollecting the carbon fiber. The process will be described forillustration purposes with reference to the apparatus shown in FIGS. 10and 11.

[0170] The carbon supply necessary to grow the SWNT molecular array intoa continuous fiber is supplied to the reactor 1000, in gaseous formthrough inlet 1002. The gas stream should be directed towards the frontsurface of the growing array 1004. The gaseous carbon-containingfeedstock can be any hydrocarbon or mixture of hydrocarbons includingalkyls, acyls, aryls, aralkyls and the like, as defined above. Preferredare hydrocarbons having from about 1 to 7 carbon atoms. Particularlypreferred are methane, ethane, ethylene, actylene, acetone, propane,propylene and the like. Most preferred is ethylene. Carbon monoxide mayalso be used and in some reactions is preferred. Use of CO feedstockwith preformed Mo-based nano-catalysts is believed to follow a differentreaction mechanism than that proposed for in situ-formed catalystclusters. See Dai.

[0171] The feedstock concentration is preferably as chosen to maximizethe rate of reaction, with higher concentrations of hydrocarbon givingfaster growth rates. In general, the partial pressure of the feedstockmaterial (e.g., ethylene) can be in the 0.001 to 10.0 Torr range, withvalues in the range of about 1.0 to 10 Torr being preferred. The growthrate is also a function of the temperature of the growing array tip asdescribed below, and as a result growth temperatures and feed stockconcentration can be balanced to provide the desired growth rates.

[0172] It is not necessary or preferred to preheat the carbon feedstockgas, since unwanted pyrolysis at the reactor walls can be minimizedthereby. The only heat supplied for the growth reaction should befocused at the growing tip of the fiber 1004. The rest of the fiber andthe reaction apparatus can be kept at room temperature. Heat can besupplied in a localized fashion by any suitable means. For the smallfibers useful in making nanoscale probes and manipulators, a laser 1006focused at the growing end is preferred (e.g., a C—W laser such as anargon ion laser beam at 514 nm). For larger fibers, heat can be suppliedby microwave energy or R—F energy, again localized at the growing fibertip. Any other form of concentrated electromagnetic energy that can befocused on the growing tip can be employed (e.g., solar energy). Careshould be taken, however, to avoid electromagnetic radiation that willbe absorbed to any appreciable extent by the feedstock gas.

[0173] The SWNT molecular array tip should be heated to a temperaturesufficient to cause growth and efficient annealing of defects in thegrowing fiber, thus forming a growth and annealing zone at the tip. Ingeneral, the upper limit of this temperature is governed by the need toavoid pyrolysis of the feedstock and fouling of the reactor orevaporation of the deposited metal catalyst. For most feedstocks, thisis below about 1300° C. The lower end of the acceptable temperaturerange is typically about 500° C., depending on the feedstock andcatalyst efficiency. Preferred are temperatures in the range of about500° C. to about 1200° C. More preferred are temperatures in the rangeof from about 700° C. to about 1200° C. Temperatures in the range ofabout 900° C. to about 1100° C. are the most preferred, since at thesetemperatures the best annealing of defects occurs. The temperature atthe growing end of the cable is preferably monitored by, and controlledin response to, an optical pyrometer 1008, which measures theincandescence produced. While not preferred due to potential foulingproblems, it is possible under some circumstances to employ an inertsweep gas such as argon or helium.

[0174] In general, pressure in the growth chamber can be in the range of1 millitorr to about 1 atmosphere. The total pressure should be kept at1 to 2 times the partial pressure of the carbon feedstock. A vacuum pump1010 may be provided as shown. It may be desirable to recycle thefeedstock mixture to the growth chamber. As the fiber grows it can bewithdrawn from the growth chamber 1012 by a suitable transport mechanismsuch as drive roll 1014 and idler roll 1016. The growth chamber 1012 isin direct communication with a vacuum feed lock zone.

[0175] The pressure in the growth chamber can be brought up toatmospheric, if necessary, in the vacuum feed lock by using a series ofchambers 1100. Each of these chambers is separated by a loose TEFLONO-ring seal 1102 surrounding the moving fiber. Pumps 1104 effect thedifferential pressure equalization. A take-up roll 1106 continuouslycollects the room temperature carbon fiber cable. Product output of thisprocess can be in the range of 10⁻³ to 10¹ feet per minute or more. Bythis process, it is possible to produce tons per day of continuouscarbon fiber made up of SWNT molecules.

[0176] Growth of the fiber can be terminated at any stage (either tofacilitate manufacture of a fiber of a particular length or when toomany defects occur). To restart growth, the end may be cleaned (i.e.,reopened) by oxidative etching (chemically or electrochemically). Thecatalyst particles can then be reformed on the open tube ends, andgrowth continued.

[0177] The molecular array (template) may be removed from the fiberbefore or after growth by macroscopic physical separation means, forexample by cutting the fiber with scissors to the desired length. Anysection from the fiber may be used as the template to initiateproduction of similar fibers.

[0178] The continuous carbon fiber of the present invention can also begrown from more than one separately prepared molecular array ortemplate. The multiple arrays can be the same or different with respectto the SWNT type or geometric arrangement in the array. Cable-likestructures with enhanced tensile properties can be grown from a numberof smaller separate arrays as shown in FIG. 12. In addition to themasking and coating techniques described above, it is possible toprepare a composite structure, for example, by surrounding a centralcore array of metallic SWNTs with a series of smaller circularnon-metallic SWNT arrays arranged in a ring around the core array asshown in FIG. 13.

[0179] The carbon nanotube structures useful according to this inventionneed not be round or even symmetrical in two-dimensional cross section.It is even possible to align multiple molecular array seed templates ina manner as to induce nonparallel growth of SWNTs in some portions ofthe composite fiber, thus producing a twisted, helical rope, forexample. It is also possible to catalytically grow carbon fiber in thepresence of an electric field to aid in alignment of the SWNTs in thefibers, as described above in connection with the formation of templatearrays.

[0180] Random Growth of Carbon Fibers From SWNTs

[0181] It is also possible to produce useful compositions comprising arandomly oriented mass of SWNTs, which can include individual tubes,ropes and/or cables. The random growth process has the ability toproduce large quantities, i.e., tons per day, of SWNT material.

[0182] In general the random growth method comprises providing aplurality of SWNT seed molecules that are supplied with a suitabletransition metal catalyst as described above, and subjecting the seedmolecules to SWNT growth conditions that result in elongation of theseed molecule by several orders of magnitude, e.g., 10² to 10¹⁰ or moretimes its original length.

[0183] The seed SWNT molecules can be produced as described above,preferably in relatively short lengths, e.g., by cutting a continuousfiber or purified bucky paper. In a preferred embodiment, the seedmolecules can be obtained after one initial run from the SWNT feltproduced by this random growth process (e.g., by cutting). The lengthsdo not need to be uniform and generally can range from about 5 nm to 10μm in length.

[0184] These SWNT seed molecules may be formed on nanoscale supportsthat do not participate in the growth reaction. In another embodiment,SWNTs or SWNT structures can be employed as the support material/seed.For example, the self assembling techniques described below can be usedto form a three-dimensional SWNT nanostructure. Nanoscale powdersproduced by these technique have the advantage that the support materialcan participate in the random growth process.

[0185] The supported or unsupported SWNT seed materials can be combinedwith a suitable growth catalyst as described above, by opening SWNTmolecule ends and depositing a metal atom cluster. Alternatively, thegrowth catalyst can be provided to the open end or ends of the seedmolecules by evaporating a suspension of the seeds in a suitable liquidcontaining a soluble or suspended catalyst precursor. For example, whenthe liquid is water, soluble metal salts such as Fe (NO₃)₃, Ni(NO₃)₂ orCO(NO₃)₂ and the like may be employed as catalyst precursors. In orderto ensure that the catalyst material is properly positioned on the openend(s) of the SWNT seed molecules, it may be necessary in somecircumstances to derivitize the SWNT ends with a moiety that binds thecatalyst nanoparticle or more preferably a ligand-stabilized catalystnanoparticle.

[0186] In the first step of the random growth process the suspension ofseed particles containing attached catalysts or associated withdissolved catalyst precursors is injected into an evaporation zone wherethe mixture contacts a sweep gas flow and is heated to a temperature inthe range of 250-500° C. to flash evaporate the liquid and provide anentrained reactive nanoparticle (i.e., seed/catalyst). Optionally thisentrained particle stream is subjected to a reduction step to furtheractivate the catalyst (e.g., heating from 300-500° C. in H₂). Acarbonaceous feedstock gas, of the type employed in the continuousgrowth method described above, is then introduced into the sweepgas/active nanoparticle stream and the mixture is carried by the sweepgas into and through a growth zone.

[0187] The reaction conditions for the growth zone are as describedabove, i.e., 500-1000° C. and a total pressure of about one atmosphere.The partial pressure of the feedstock gas (e.g., ethylene, CO) can be inthe range of about 1 to 100 Torr. The reaction is preferably carried outin a tubular reactor through which a sweep gas (e.g., argon) flows.

[0188] The growth zone may be maintained at the appropriate growthtemperature by 1) preheating the feedstock gas, 2) preheating the sweepgas, 3) externally heating the growth zone, 4) applying localizedheating in the growth zone, e.g., by laser or induction coil, or anycombination of the foregoing.

[0189] Downstream recovery of the product produced by this process canbe effected by known means such as filtration, centrifugation and thelike. Purification may be accomplished as described above.

[0190] The carbon nanotubes prepared by the above described process mayalso employ the hexaboronitride lattice. This material formsgraphene-like sheets with the hexagons made of B and N atoms (e.g., B₃N₂or C₂BN₃). It is possible to provide an outer coating to a growingcarbon fiber by supplying a BN precursor (e.g, tri-chloroborazine, amixture of NH₃ and BCl₃ or diborane) to the fiber which serves as amandrel for the deposition of BN sheets. This outer BN layer can provideenhanced insulating properties to the metallic carbon fiber of thepresent invention. Outer layers of pyrolytic carbon polymers or polymerblends may also be employed to impart insulating properties. By changingthe feedstock in the above described process from a hydrocarbon to a BNprecursor and back again it is possible to grow a fiber made up ofindividual tubes that alternate between regions of all carbon latticeand regions of BN lattice. In another embodiment, an all BN fiber can begrown by starting with a SWNT template array topped with a suitablecatalyst and fed BN precursors. These graphene and BN systems can bemixed because of the very close match of size to the two hexagonal unitsof structure. In addition, they exhibit enhanced properties due to theclose match of coefficients of thermal expansion and tensile properties.

[0191] While the invention has been particularly shown and described bythe foregoing detailed description, it will be understood by thoseskilled in the art that various other changes in form and detail may bemade without departing from the spirit and scope of the invention.

What is claimed is:
 1. An article of manufacture comprising amacroscopic mounting element capable of being manipulated or observed ina macroscale environment and a nanoscale nanotube assembly attached tosaid mounting element, whereby said article permits macroscaleinformation to be provided to or obtained from a nanoscale environment.2. The article of claim 1 wherein said mounting element is adapted tosupport and move said nanotube assembly.
 3. The article of cam whereinsaid mounting element is adapted to provide an electrical connection tosaid nanotube assembly.
 4. The article of claim 1 additionallycomprising detection means operatively associated with said mountingelement for detecting information obtained by said nanotube assembly insaid nanoscale environment.
 5. The article of claim 4 wherein saiddetection means is selected from the group consisting of electronic,electromechanical and optical means.
 6. The article of claim 5 whereinsaid electromechanical detection means is a piezoelectric deflectionsystem.
 7. The article of claim 1 wherein said mounting element is aproximity probe cantilever.
 8. The article of claim 1 wherein saidmounting element is a proximity probe tip.
 9. The method of claim 7 or 8wherein said proximity probe is adapted for use in a microscopy systemselected from the group consisting of STM, AFM and MFM.
 10. The articleof claim 1 wherein said nanoscale nanotube assembly comprises a singlenanotube.
 11. The article of claim 10 wherein said single nanotube is acarbon nanotube.
 12. The article of claim 11 wherein said carbonnanotube is selected from single-wall carbon nanotubes and multi-wallcarbon nanotubes.
 13. The article of claim 11 wherein said carbonnanotube is a single-wall carbon nanotube.
 14. The article of claim 11wherein said single-wall carbon nanotube has insulating properties. 15.The article of claim 11 wherein said single-wall carbon nanotube hasmetallic properties.
 16. The article of claim 15 wherein saidsingle-wall carbon nanotube has arm chair (n,n) configuration.
 17. Thearticle of claim 15 wherein said single-wall carbon nanotube has a(10,10) configuration.
 18. The article of claim 11 wherein said carbonnanotube is doped with non-carbon atoms in the fullerene lattice. 19.The article of claim 11 wherein said carbon nanotube contains anendohedrally located species.
 20. The article of claim 19 wherein saidendohedrally located species is selected from metals, ions, smallmolecules and fullerenes.
 21. The article of claim 20 wherein saidspecies is a paramagnetic material.
 22. The article of claim 20 whereinsaid species is a ferromagnetic material.
 23. The article of claim 11wherein said carbon nanotube is derivitized with a chemical moiety. 24.The article of claim 23 wherein said chemical moiety is bound to saidcarbon nanotube at a position on the side of said nanotube.
 25. Thearticle of claim 23 wherein said chemical moiety is bound to the end capof said nanotube.
 26. The article of claim 1 wherein said nanotubeassembly comprises a plurality of generally parallel nanotubes.
 27. Thearticle of claim 26 wherein said nanotubes are carbon nanotubes.
 28. Thearticle of claim 26 or 27 wherein said plurality of nanotubes is abundle having from about 2 to about 10³ individual nanotubes.
 29. Thearticle of claim 26 or 27 wherein said plurality of nanotubes is a ropehaving from about 10³ to 10⁶ individual nanotubes.
 30. The article ofclaim 26 or 27, wherein said nanotube assembly comprises a body sectionand a tip section comprising from about 1 to about 10 individualnanotubes projecting beyond said body section.
 31. The article of claim1 wherein said nanotube assembly has a length of from about 20 to 100times its diameter.
 32. The article of claim 1 wherein said nanotubeassembly is attached to said mounting element at one end and the otherend of said nanotube assembly freely projects from said mountingelement.
 33. The article of claim 1 which is a probe for providinginformation from a nanoscale environment.
 34. The article of claim 33which is a probe adapted for use in a proximity probe microscopy system.35. The probe of claim 34 wherein said proximity probe microscopy systemis STM.
 36. The probe of claim 34 wherein said proximity probemicroscopy system is AFM.
 37. The probe of claim 34 wherein saidproximity probe microscopy system is MFM.
 38. The article of claim 34wherein said probe is adapted to image a surface at nanoscaleresolution.
 39. The article of claim 34 wherein said probe is adapted tomeasure properties of nanoscale objects.
 40. The article of claim 39wherein said probe is adapted to measure the elasticity of nanoscaleobjects.
 41. The article of claim 39 wherein said probe is adapted tomeasure atomic scale friction of nanoscale objects.
 42. The article ofclaim 39 wherein said probe is adapted to measure electronic propertiesof nanoscale objects.
 43. The article of claim 39 wherein said probe isadapted to measure magnetic properties of nanoscale objects.
 44. Thearticle of claim 39 wherein said probe is adapted to measureelectrochemical properties of nanoscale objects.
 45. The article ofclaim 39 wherein said probe is adapted to measure chemical properties ofnanoscale objects.
 46. The article of claim 39 wherein said probe isadapted to measure biological properties of nanoscale objects.
 47. Thearticle of claim 46 wherein said probe is adapted to analyzebiomolecules and components thereof.
 48. The article of claim 47 whereinsaid probe is adapted to sequence DNA molecules by recognizingindividual base moieties.
 49. The article of claim 1 which is a probefor manipulating or modifying a nanoscale object.
 50. The article ofclaim 49 wherein said probe is adapted to move a nanoscale object. 51.The article of claim 49 wherein said probe is adapted to modify ananoscale surface by creating a pattern on the surface of said object.52. The article of claim 51 wherein said probe is adapted to performnanolithography.
 53. The article of claim 49 wherein said probe isadapted to chemically modify said nanoscale object.
 54. The article ofclaim 53 wherein said probe contains a chemical moiety attached to itstip to induce said chemical modification.
 55. The article of claim 53wherein said probe is adapted to emit electrons to induce said chemicalmodification.
 56. The article of claim 53 wherein said probe is adaptedto emit electromagnetic radiation to induce said chemical modification.57. The article of claim 54 wherein said chemical moiety is a speciesthat reacts with species on the surface of said nanoscale object. 58.The article of claim 54 wherein said chemical moiety is a catalyst for areaction that takes place on the surface of said nanoscale object. 59.The article of claim 1 which is a tool for the fabrication of nanoscaledevices.
 60. The article of claim 1 wherein at least a portion of saidnanotube assembly is coated with a material selected from the groupconsisting of thermosetting polymers, thermoplastic polymers, UV curingpolymers, silicon and metals.
 61. The method of claim 60 wherein saidcoating also covers at least a portion of said mounting element.
 62. Thearticle of claim 1 comprising an array of nanotube assemblies attachedto mounting elements.
 63. The article of claim 62 wherein said nanotubeassemblies are each attached to separate mounting elements.
 64. Thearticle of claim 63 wherein said nanotube assemblies are attached to acommon mounting element.
 65. A method for making a macroscopicallymanipulable nanoscale device comprising: providing a nanotube-containingmaterial; preparing a nanotube assembly having at least one nanotube;and attaching said nanotube assembly to a ice of a mounting element. 66.The method of claim 65 wherein said nanotube is a carbon nanotube. 67.The method of claim 65, further comprising coating a portion of saidnanotube assembly with a metal.
 68. The method of claim 65, wherein saidstep of preparing a nanotube assembly comprises: contacting saidnanotube-containing material with an adhesive member, and removing saidadhesive member from said nanotube-containing material, whereby aplurality of nanotubes are oriented perpendicular to said surface ofsaid nanotube-containing material.
 69. The method of claim 65, whereinsaid step of attaching said nanotube assembly to a surface of a mountingelement comprises: translating said mounting element toward saidnanotube assembly; contacting said mounting element and said nanotubeassembly; and translating said mounting element away from said nanotubeassembly.
 70. The method of claim 65, wherein nanotube assembly and saidmounting element are attached by van der Waals forces.
 71. The method ofclaim 65, wherein said nanotube assembly and said mounting element areattached by adhesive bonding.
 72. The method of claim 69 wherein aportion of said mounting element is coated with an adhesive prior tocontact with said nanotube assembly.
 73. The method of claim 72, whereinsaid adhesive is an acrylic adhesive.
 74. The method of claim 66,wherein said surface of said mounting device is highly graphitizedcarbon.
 75. The method of claim 65, further comprising coating thenanotube assembly attached to said mounting element.
 76. The method ofclaim 75, wherein said coating is applied by dipping.
 77. The method ofclaim 75, wherein said coating is applied by vapor phase deposition. 78.The method of claim 75, wherein said coating is selected from the groupconsisting of cyanoacrylate, methacrylate, Parylene®, polyimide,silicon, silica and metals.
 79. The method of claim 65 wherein saidattaching step is performed under observation using an opticalmicroscope.
 80. A method for imaging an object at nanoscale resolutioncomprising scanning the surface of said object with a proximity probemicroscopy apparatus having a probe tip that comprises a nanoscalenanotube assembly.
 81. A method for manipulating or modifying nanoscaleobjects comprising bringing a probe tip comprising a nanoscale nanotubeassembly into contract with or proximity to said nanoscale objects andactuating an interaction between said probe tip and said nanoscaleobject.
 82. The method of claim 81 wherein said interaction is by directphysical contact.
 83. The method of claim 81 wherein said interaction iseffected by indirect means selected from the group consisting ofelectronic, chemical, mechanical, electrochemical, electromechanical,electromagnetic, magnetic and biological.